As an LSI device or a memory device is miniaturized, a depth of a diffusion layer in a transistor manufacturing process is decreased. Conventionally, doping atoms implanted into the diffusion layer are activated by a high-speed heating process referred to as an RTA (Rapid Thermal Annealing) using a lamp heater. However, in the RTA process, as the diffusion of the doping atoms progresses, the depth of the diffusion layer exceeds a tolerable range, and this makes the miniaturized design difficult. Since the depth of the diffusion layer is incompletely controlled, the electrical characteristics of devices deteriorate. For example, a problem such as occurrence of leakage current or the like is generated.
Recently, an apparatus using microwaves has been suggested as an apparatus for heating a semiconductor wafer. When doping atoms are activated by microwave heating, a microwave directly acts on the doping atoms. Hence, excessive heating does not occur, and the diffusion of the diffusion layer can be suppressed.
As for the heating apparatus using microwaves, a microwave heating apparatus in which a specimen is heated by introducing microwaves into a pyramid-shaped horn through a rectangular waveguide is suggested in, e.g., Japanese Patent Application Publication No. S62-268086. In this reference, the rectangular waveguide and the pyramid-shaped horn are arranged at an angle of about 45° in an axial direction, so that two orthogonally polarized microwaves in a TE10 mode can be radiated to the specimen at the same phase.
In Japanese Utility Model Application Publication No. H6-17190, a microwave heating apparatus including a heating chamber having a square cross section whose size is set to about λ/2 to λ of a free space wavelength of the introduced microwaves is suggested as a heating apparatus for bending a heating target object.
When doping atoms are activated by microwave heating, it is required to supply a power larger than a certain level. Accordingly, microwaves may efficiently be introduced into a processing chamber by providing a plurality of microwave introduction ports. When a plurality of microwave introduction ports is provided, microwaves introduced from one of the microwave introduction ports may enter another microwave introduction port, thereby deteriorating power usage efficiency and heating efficiency
In the case of microwave heating, the microwaves are directly irradiated to a semiconductor wafer disposed immediately below the microwave introduction ports, so that the surface of the semiconductor wafer is not uniformly heated.